overhead of plpgsql functions over simple select

I'd like to encapsulate something that now is just a simple select
in a plpgsql function now just to keep an interface consistent but
even for well... encapsulating the sql.

Right now a simple select statement will suffice.

What kind of overhead a plpgsql that just return a select incur
compared to a simple select?

I'm not that worried of old query plans.

thx

--
Ivan Sergio Borgonovo
http://www.webthatworks.it